Over the years, a variety of positive feed devices have been developed for use in multifeed knitting machines, to assure that, during the operation of the machine, predetermined increments of yarn will be fed from the yarn packages to the machine needles. One of the most widely used mechanisms of this type is described in Rosen U.S. Pat. No. 3,090,215 wherein the positive feed device comprises a plurality of rollers having an endless tape running over the surface of the rollers and driven by the machine during its normal operation, with the yarns being supplied by appropriate guide means to locations between the tape and roller surfaces so as to be positively fed as the tape is driven. In a variation of this general structure, shown for example in Rosen U.S. Pat. No. 3,264,845, and Deniega U.S. Pat. No. 3,802,228, the tape is made narrower than the running surface of the roller, and the yarn guide is arranged to be selectively displaced between a first position located under the tape to effect positive feeding of the yarn, and a second position which is axially displaced from the tape to stop the yarn feed. These variations in structure are provided for "stop-motion" purposes, i.e., while the yarn is normally located under the tape of the feed device, if the yarn should break an operator can manually displace the yarn guide of each yarn feed device to stop the yarn feeding operations and/or, particularly if a mechanism is provided which detects a yarn break, to completely stop operation of the machine. Other positive feeding arrangements capable of achieving these same general results are described in Rosen U.S. Pat. Nos. 3,419,225 and 3,796,384, Tannert U.S. Pat. No. 3,709,444, and Jacobsson U.S. Pat. No. 3,791,599.
Roller/tape positive feeding devices of the general type described above have been widely adopted for use in a number of different types of knitting machines, but have not been considered practical for use in machines where it is required that different yarns be selectively fed to the machine on a demand basis. In machines of this latter type, one example being the so-called striping machine wherein a plurality of differently colored yarns are fed to a common striping box which functions, as the machine operates, to demand successively different ones of said yarn in a predetermined repetitive sequence, conventional roller/tape positive feeding devices have been considered incapable of accommodating the changing demands of the machine due to the fact that such devices do not have the facility to respond in a bi-directional manner to the demand or lack of demand of a given yarn. In a still further arrangement described in Nance U.S. Pat. No. 3,418,831, an effort has been made to adapt the Rosen-type positive feeding device to machines operating on a demand basis, through the provision of mechanisms taking the form of elongated rods and/or signal responsive solenoids intended to shift the yarn guide of the positive feed device between feed and nonfeed positions in dependence upon the changing demands of the knitting machines. Devices of the Nance type, however, are extremely complex and costly to install and maintain, and therefore have not found any general acceptance in the knitting machine field.
The present invention provides an improved form of roller/tape positive feed device which is adapted to positively feed yarn to a knitting machine on a selective basis responsive to the demands of the machine, and which is capable of achieving such positive demand feeding in an arrangement which is completely automatic in operation and far simpler, less costly, and more reliable than structures suggested heretofore e.g., of the aforementioned Nance type.